1. Field of the Invention
This invention relates to systems for producing purified water from feed water, and more particularly to a filter cartridge including a reverse osmosis filter, and to water filtration apparatus including such a filter.
2. Description of the Prior Art
Drinking-water purification systems have found increasing use in the home and the work place to improve the quality of tap water for drinking, cooking, ice-making and the like. "Reverse osmosis processes" are a known class of processes in general use in these systems. The processes employ "reverse osmosis membranes" which are selectively impermeable to dissolved salts in aqueous solution. Some prior-art purification systems include, in addition to the reverse osmosis membrane permeator, a prefilter for initial screening of the feed water, removing particulate matter to prevent clogging and to protect the membrane, and a post-filter for further purification, especially for the removal of organics such as dissolved hydrocarbons. In general, in these systems feed water, usually in the form of tap water, is filtered and separated as purified product water and waste water.
Reverse osmosis membrane permeators constitute a major restriction to the flow of water through these purification systems, and so the filtration process is relatively slow. Therefore, a system which is economically and aesthetically practical for the home is generally unable to generate product water on demand but must include a product water storage reservoir. Pressures within the system require control to optimize the system operation. Finally, waste water must be disposed of.
While a water-purification system will include a control-valve subsystem, a reverse osmosis filtration apparatus and a product water reservoir, this invention is directed to a cartridge and filtration apparatus including such a cartridge.
The prior art includes U.S. Pat. No. 3,789,993, 3,792,135 and 3,824,299 to Brown and Ray. These patents disclose the specifics of composition and manufacture of reverse osmosis membrane permeators which may be used in embodiments of this invention. The prior art also includes U.S. Pat. No. 3,504,796 and 3,542,199 to Bray, which disclose a particular configuration and combination of prefilter, membrane permeator and post-filter in a water-purification system. These prior-art items are background to this invention and are incorporated by reference herein.
The reverse osmosis water purification unit described in U.S. Pat. Specification No. 3,542,199 has the disadvantages that connections to it have to be broken when it is necessary to change filter components, for example, when they are exhausted, and remade after the substitution of new filter components. Obviously, at least from the aspect of domestic usage, the need for breaking and remaking of connections is very unattractive to potential purchasers, very undesirable to existing owners and may have tragic consequences.
U.S. Pat. Specification No. 4,218,317 describes a water purifier which is intended to stand on a counter top. It has flexible hose connections for supply of feed-water, for waste water to drain and for purified water. Two connections are at one end of the purifier housing and one connection is at the other end of the housing. The housing is formed by two housing parts which screw-threadedly engage one another at the middle of the length of the housing. Thus, while connections do not have to be broken and remade when changing filter cartridges, because they are flexible, the connections do have to be flexible if breaking and remaking connections are to be avoided, and flexible hoses are undesirable from the viewpoint of longtime trouble-free service.
It is an object of the present invention to render it unnecessary to break and remake connections when changing a filter cartridge or to use flexible connections.